US 2007/0104789 A1 describes gastro-resistant and ethanol-resistant controlled-release formulations comprising hydromorphone. The gastro-resistant and ethanol-resistant can be used in a matrix as well as the coating of the formulations. Alginic acid is mentioned among the examples for suitable gastro-resistant and -ethanol resistant substances. Pellet cores or granules may be prepared by anhydrous granulation, may be coated with the gastro-resistant and ethanol-resistant substances and then may be filled in capsules or bags or compressed into tablets under addition of dried pharmaceutical or nutraceutically acceptable auxiliary substances.
WO 2012/022498 describes a gastric resistant pharmaceutical or nutraceutical composition, comprising a core, comprising a pharmaceutical or nutraceutical active ingredient and a gastric resistant coating layer onto the core, wherein the release of the pharmaceutical or nutraceutical active ingredient is not more than 15% under in-vitro conditions at pH 1.2 for 2 hours in a buffered medium according to USP with and without the addition of 40% (v/v) ethanol, wherein the gastric resistant coating layer comprises 10 to 100% by weight of one or more salts of alginic acid with a viscosity of 30 to 720 cP of a 1% aqueous solution. The one layer system as described solves the problem protection against the influence of ethanol. However except for coatings which include the ammonium alginate, coatings which employ other alginate salts, like sodium or potassium alginate, show no resistance against the influence of calcium ions at the same time.